Recent evidence indicates that invasion of pancreatic ductal adenocarcinoma (PDAC) cells in 3D collagen depends on G?13, a member of the G12 family of heterotrimeric G proteins, and can be reversed by the collagen-binding protein discoidin domain receptor 1 (DDR1). The long-term goal is to contribute toward the development of novel mechanism-based targeted therapies for the treatment of PDAC. The main objective in this application is to determine how G?13 contributes to PDAC progression in vivo. The central hypothesis is that G?13 enhances PDAC progression by disrupting DDR1-mediated cell-cell adhesion and by activating YAP1 signaling. A second hypothesis is that G?13 enhances inflammation that is present in PDAC tumors. These hypotheses are based on extensive preliminary data demonstrating that G?13 knockdown decreases invasion in 3D collagen, decreases YAP1 signaling, and enhances E-cadherin-mediated cell-cell adhesion. In addition, loss of the polarity protein Par3, which can function downstream of DDR1, enhances YAP1 signaling and promotes invasion of PDAC cells in 3D collagen. Moreover, G?13 regulates HMGA2, which can mediate chemoresistance, and also regulates in PDAC cells stem cell factor (SCF), which can mediate mast cell migration. The rationale for the proposed research is that a determination of the effect and underlying mechanism of G?13 in PDAC progression in vivo is likely to provide strong justification for the continued development of G?13 and its downstream effectors as targets for novel anti-PDAC therapy. Three specific aims are proposed: 1) Determine the role of G?13 in PDAC progression in vivo; 2) Determine the role of G?13 in mediating PDAC inflammation in vivo; and 3) Determine the mechanism by which DDR1 counteracts G?13 in PDAC cells in vivo. Under the first aim, the effects of knocking out G?13 on limiting tumor progression and increasing response to chemotherapy will be evaluated in mouse models and in human PDAC organoids. The role of YAP1 in G?13-mediated PDAC progression and the mechanism by which G?13 mediates chemo- resistance will be evaluated. For the second aim, the mechanism by which G?13 in PDAC cells enhances SCF expression and mast cell migration will be characterized. In addition, the effects of modulating G?13 in vivo on other inflammatory cells will also be determined. In the third aim, the role of Par3 in mediating tumor progression in mouse models and in human PDAC organoids will be evaluated. The extent to which Par3 functions downstream of DDR1 to attenuate the effects of G?13 on PDAC progression will also be determined. The research proposed is innovative because it utilizes complex models, including 3D acinar cultures, human PDAC organoids, and transgenic and orthotopic mouse models, to delineate the role of G?13 and Par3 in PDAC progression. This proposed research is significant because it will provide a mechanistic determination of the role of G?13 in mediating tumor progression and chemoresistance, and also PDAC inflammation, subsequently creating new opportunities for the development of innovative therapies to treat PDAC patients.